For the past couple weeks, Vice President Joe Biden and a bipartisan group of lawmakers have held a series of meetings. Their mission: Find money in the federal budget that can be cut and thus pave the way for Congress to raise the debt ceiling.

While lawmakers have been uncharacteristically silent on how negotiations are going, Biden let it slip that the group is looking to find cuts in the $1 trillion range.

"We're in a position where we will be able to get well above a trillion dollars pretty quick," he told reporters.

Most budget experts think the government needs to find savings of around $4 trillion over the next decade to get back on a sustainable path, but $1 trillion in cuts over the same time period would be a nice down payment.

"I take them at their word they are looking at $1 trillion," said Marc Goldwein, policy director for Committee for a Responsible Federal Budget. "That would be an excellent start."

And what exactly is on the chopping block? Details are thin, but clues can be found by comparing President Obama's budget plan with that of House Republicans, and other fiscal plans that have gained traction in Washington.

The cuts are likely to come from areas where the plans overlap.

One popular idea: Limiting discretionary spending through the establishment of a "cap" that would, at some point, force lawmakers to make hard choices on spending.

Both Obama and Paul Ryan, the House budget chairman, favor a mechanism along those lines. Of course, Republicans and Democrats likely differ on the details, like which programs to cut and what level spending should be capped at.

Depending on the final outline, CRFB estimates the 10-year savings from a cap could be as high as $1.6 trillion, or as low as $580 billion.

That's by far the biggest source of savings. But there are about a dozen other proposals that would yield substantial savings.

One option likely to make the final plan is asking federal workers to contribute more to their pension plans. That would save between $65 billion to $120 billion over ten years, according to CRFB.